Synthesis of Metal Chalcogenides Nano Structured Films by AACVD Technique using Metal Organophosphinate Complexes as Single Source Precursors and Their Dielectric Studies

Abstract

Metal chalcogenides (sulfides, selenides, and tellurides) have become potent candidates for many technological applications and finding their employment in many fields like the manufacturing of capacitors, waveguides, storage memories, bio and chemical sensors etc. Synthesis of semiconducting metal sulfide/selenide thin films as well as nanostructures, generally implicates the decomposition of various types of organometallic precursors. The major aim of present study was to synthesize metal organophosphinate precursors, to grow metal sulfide and selenide nanostructures by aerosol assisted chemical vapor deposition (AACVD) of these complexes and to investigate structural, morphological, and dielectric properties of synthesized nanostructures. This study reports the synthesis of bis(diisobutyldithiophosphinato) lead(II) [Pb(iBu2PS2)2], bis(diisobutyldithiophosphinato) nickel (II) [Ni(iBu2PS2)2] and diphenyldiselenophosphinate lead (II) [Pb(iPh2PSe2)2] complexes. Various analytical tools including elemental analysis, mass spectrometry, Infrared spectroscopy (IR), Nuclear magnetic resonance spectroscopy (NMR), and Thermogravimetric analysis (TGA) were also employed to confirm the successful synthesis of the precursors. These single-source precursors were decomposed using the AACVD technique at different temperatures (350 - 500 ℃) to grow PbS, NiS and PbSe nanostructures on glass substrates, respectively. Resultant semiconductor thin depositions were characterized by the X-ray diffraction method (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) analysis. Their impedance and dielectric properties were also studied to explore the scope of these nanostructures in the field of electronics. Impedance spectroscopic measurements were performed for PbS in the frequency range of 40 Hz to 6 MHz at room temperature. In a complex impedance plane plot, two relaxation processes were exhibited due to grains and grain boundaries contribution. A high value of dielectric constant was observed at low frequencies, which was explained based on Koops phenomenological model and Maxwell–Wagner type polarization. Frequency-dependent AC conductivity results were compliant with Jonsher’s power law, while the capacitance-voltage loop had a butterfly shape. These impedance spectroscopic results have corroborated the ferroelectric nature of the resultant PbS nano deposition. The Dielectric studies of NiS were carried out at room temperature within the 100 Hz to 5 MHz frequency range. Maxwell-Wagner model gave a complete explanation of the variation of dielectric properties along with frequency. The reason behind high dielectric constant values at low frequency was further endorsed by Koops phenomenological model. The efficient translational hopping and futile reorientation vibration caused the overdue exceptional drift of AC conductivity (σac) along with the rise in frequency. Two relaxation processes caused by grains and grain boundaries were identified from the fitting of a complex impedance plot with an equivalent circuit model (Rg Cg) (Rgb Qgb Cgb). Asymmetry and depression in the semicircle having center present lower than the impedance real axis gave solid justification of dielectric behavior that is non-Debye in nature. Characteristic dielectric measurements along with impedance spectroscopic analysis for obtained PbSe were executed at room temperature within frequency range variation between 100 Hz – 5 MHz. The dielectric constant and dielectric loss gave similar behavior along with altering frequency which was well explained by Koops theory and Maxwell–Wagner theory. The effective short range translational hopping gave rise to an overdue remarkable increase in AC conductivity (σac) accompanied by frequency elevation. Fitting of a complex impedance plot was carried out with an equivalent circuit model (Rg Cg) (Rgb Qgb Cgb), which proved that grains as well as grain boundaries are responsible for two relaxation processes. Asymmetric depressed semicircle with center lower to impedance real axis gave clear explanation of non- Debye dielectric behavior. In summary, subject study has concluded that nanostructures of PbS, NiS and PbSe prepared by AACVD of their metal organophosphinate single-source precursors, have shown decrease in dielectric constant and increase in AC conductivity at higher frequency, making them significant candidates in the field of high frequency devices.